1. Filed of the Invention
The present invention relates to an image information network, and more specifically to an image information network wherein a visual characteristic of an image output by an image reproducing apparatus is improved.
2. Description of the Related Art
Recently, radiation image reading recording systems (Computed Radiography systems or CR systems) have been widely spread and put into practice. Stimulable phosphor, which emits light upon exposure to stimulating rays such as visible light or a laser beam in accordance with radiation energy originated in a radioactive ray having been irradiated on the material and stored therein, is used for a CR system. A CR system temporarily records radiation image information regarding a subject such as a human body on a stimulable phosphor sheet, and scans the stimulable phosphor sheet using a stimulating ray such as a laser beam to cause the sheet to emit light. The emitted light is read photoelectrically as an electric signal and the CR system obtains this image signal. After carrying out predetermined image processing on the image signal, the CR system outputs a visible image.
The CR system includes a display apparatus for displaying the resultant visible image, a laser printer (LP) for outputting the image on a film, and the like. In order to cause the resultant visible image to become optimal for diagnosis, predetermined image processing such as frequency enhancing processing, tone processing, enlargement or reduction processing accompanied by interpolation processing (hereinafter simply called xe2x80x9cinterpolation processingxe2x80x9d), and the like is generally carried out on the image signal before the output thereof.
In a CR system, the enlargement or reduction processing to which the interpolation processing is applied is pre-set so that a predetermined response characteristic can be obtained in accordance with a reading density, an image size, an enlargement or reduction ratio, and the like. As the interpolation processing applied to the enlargement or reduction processing, interpolation methods which find a value of one signal based on values of 2 signals (for example, linear interpolation), or based on values of 3 signals (for example, secondary Lagrange interpolation), or based on values of 4 signals (for example, a cubic spline interpolation operation; see U.S. Ser. No. 08/679,830 by the assignee) are used. Based on a characteristic of an image signal and accumulated experience in the past, the enlargement or reduction processing is set in order to obtain a visible image which is optimal for diagnosis by a simple operation.
In the field of medicine, not only the CR systems but also various kinds of medical image generating systems using X rays or the like are used. For example, CT (Computed Tomography) systems, MRI (Magnetic Resonance Imaging) Systems, and the like have been put into practice. In an image generated by each of these systems (modalities), characters showing the photographed portion and the name of a patient are included together with the subject. Therefore, it is appropriate for each of these systems to carry out enlargement or reduction processing (see U.S. Ser. No. 08/829,471 by the applicant; hereinafter called xe2x80x9cA-VRS interpolation processingxe2x80x9d) adopting interpolation processing wherein interpolation operations change sharpness continuously, ranging from high (the cubic spline interpolation operation and the like) to low (for example, a B spline interpolation operation).
Therefore, even in the case where the same image information is reproduced, an image reproduced through interpolation processing thereon by the CR system and an image reproduced through interpolation processing thereon by the A-VRS interpolation processing are visually different in terms of a frequency response characteristic.
Following the recent development and advancement of techniques in communications and computers, image information networks using computers have been constructed in hospitals, and each of the above systems, such as CR, CT, MRI systems or the like, which has been used in a stand alone mode is becoming a portion of the image information network. A network printer, which is a general purpose image reproducing apparatus and outputs images of the various apparatuses in the above, is connected to such an image information network. Furthermore, an image processing apparatus which can carry out general interpolation processing is also connected. The A-VRS interpolation processing is appropriate for the general interpolation processing.
The interpolation processing according to the A-VRS interpolation method can freely adjust the frequency response characteristic of an image in accordance with the enlargement or reduction ratio. Therefore, this processing is convenient in an attempt to obtain an optimal image by changing the frequency response characteristic by trial and error. However, it is very time-consuming to find the optimal characteristic for each image, and an operator is forced to carry out troublesome adjustment operations. Especially, for image information obtained by a CR system which has established, for each enlargement or reduction ratio, a frequency response characteristic optimal for diagnosis, there are few merits of outputting the image by a network printer after such a time-consuming operation.
Furthermore, even when the same image information is used, an image reproduced by a CR system printer after interpolation processing thereon by the CR system and an image reproduced by a network printer after the A-VRS interpolation processing thereon have a visual characteristic (frequency response characteristic) difference, which is not preferable for diagnostic purposes.
Based on considerations of the above problems, an object of the present invention is to provide an image information network which can easily obtain an image whose frequency response characteristic almost agrees visually to the frequency response characteristic of an optimal diagnostic image obtained by interpolation of a kind other than the kind of interpolation processing on the former image, by using an image processing apparatus for carrying out general interpolation processing wherein the frequency response characteristic is freely adjustable regardless of an enlargement or reduction ratio.
In an image information network (such as a medical image information network according to the DICOM [Digital Imaging and Communications in Medicine] standard) which comprises first enlargement or reduction processing means for enlarging or reducing an image represented by image information input thereto, by carrying out first interpolation processing (general interpolation processing such as the A-VRS interpolation method) which converts the image information to an image having an arbitrary enlargement or reduction ratio and an arbitrary frequency response characteristic, a first image reproducing apparatus (a general purpose network printer, for example) for reproducing the image represented by the image information input thereto from the first enlargement or reduction processing means, second enlargement or reduction processing means for carrying out enlargement or reduction processing on an image represented by image information input thereto, by carrying out second interpolation processing (such as linear interpolation) which converts the image information into image information having an enlargement or reduction ratio (including a reading density, an image size, and the like) and a frequency response characteristic both of which are pre-set stepwise and different from a conversion characteristic of the first interpolation processing, and a second image reproducing apparatus (such as a printer attached to a CR system) for reproducing the image represented by the image information input thereto from the second enlargement or reduction processing means, the image information network of the present invention is characterized by that it further comprises:
conversion means for converting the characteristic of the first interpolation processing to a characteristic corresponding to that of the second interpolation processing so that the image reproduced by the first image reproducing apparatus through the first interpolation processing almost agrees visually with the image reproduced by the second image reproducing apparatus through the second interpolation processing, in terms of the enlargement or reduction ratio and in the frequency response characteristic.
xe2x80x9cThe second interpolation processing which converts the image information into image information having an enlargement or reduction ratio and a frequency response characteristic both of which are pre-set stepwisexe2x80x9d means a linear interpolation operation, secondary Lagrange interpolation, a cubic spline interpolation operation, and the like. The second interpolation processing is processing wherein the frequency response characteristic is explicitly determined for each combination of the enlargement or reduction ratio, the reading density, the image size, and the like. In the second interpolation processing, the combination of the enlargement or reduction ratio and the like is not continuously defined, but discretely defined, such as in 10 steps, for example.
The conversion means may be a table relating the characteristic of the first interpolation processing (or a parameter defining the characteristic) to that of the second interpolation processing (or a parameter defining the characteristic), or conversion means of a known kind.
The situation wherein the images visually agree in terms of the enlargement or reduction ratio and the frequency response characteristic means that the enlargement or reduction ratios need to agree approximately, but the frequency response characteristics do not need to agree in all frequency ranges. The frequency response characteristics have to agree approximately, at least in a frequency range lower than a Nyquist frequency upon sub-sampling in the enlargement or reduction processing.
According to the image information network of the present invention, the first enlargement or reduction processing means, which carries out the general interpolation processing wherein the frequency response characteristic is freely adjustable regardless of the enlargement or reduction ratio, can generate an image which visually agrees, in terms of the frequency response characteristic, with an optimal diagnostic image obtained by interpolation processing of a kind other than the kind of the first interpolation processing, by converting the characteristic of the first interpolation processing to a characteristic corresponding to that of the second interpolation processing so that the image reproduced by the first image reproducing means through the first interpolation processing visually agrees with the image reproduced by the second image reproducing means through the second interpolation processing in terms of the enlargement or reduction ratio and the frequency response characteristic.
Therefore, for image information obtained by a CR system or the like which has established, for each enlargement or reduction ratio, the frequency response characteristic that is optimal for diagnosis, an image whose quality is almost the same visually as the quality of an image by the CR system can be output easily by a general purpose network printer, without a time-consuming operation.